A Question About Hydrofoils and Outboards

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Mark Hofman

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We have a Mariner 25 hp, electric start outboard on a 16-foot Tracker Sportsman jon boat. It pushes it along on plane with two people really well (20 to 25 mph), and with three people it will still get up on top. We added a Stingray Jr. hydrofoil and what a difference! It pops up on plane much faster and can stay on plane at much lower speeds.



My question is this: have any of you put any kind of hydrofoil on your bigger outboards, and if so would you do it again on a new boat? I'm considering putting a regular Stingray foil on a Merc 150. Other suggestions? Would you discourage it?



My reason for wanting to do this are two-fold: planing at lower speeds, and getting up on plane faster in some of the shallower lakes and rivers I fish.



Opinions are GREATLY appreciated. Thanks!



Mark
 
I put a hydrofoil on my 97 912 savage 225 EFI. Like you said What a difference in hole shot. The only problem is it is pretty dangerous turning sharp at high speed. I have since added a 10" jackplate and it has given me not only a good hole shot but also better handling and speed. The hydrofoil is great but be careful in sharp turns. Although the hydofoil is above the water after plane it will grab in sharp turns.
 
I added a Doel-Fin to my 115 Merc on a 180TF, and it made a world of difference in hole shot and planing at low speeds. I have noticed no ill-effects whatsoever, and it has made my boat a pleasure to drive rather than a hassle in shallow water.
 
Gary:



When you say, "it will grab in sharp turns", what do you experience? I picture a hard pull on the steering wheel in the direction of the turn. Is it enough to pull the wheel out of your hand? On the jon boat, we have a tiller motor, and we don't go fast enough to notice such a pull. Also, hard turns at what speeds? I typically drop down below 30 to make a really sharp turn.



Mark
 
It was a very hard pull that almost pulled the wheel out of my hands. I have a hot foot and foot trim so I was lucky I had both hands on the wheel. I was only doing 55 and it wasn't an extra sharp turn. I also talked to a champion owner that had the same thing happen. It was an emergency turn or I wouldn't have tried to turn at that speed. Glad I wasn't doing 70. I really liked the way my boat drove with it though. And it was a lot cheaper than the jackplate.
 
Watch me kill THIS thread!



I just saw on another message board that drilling holes in the cavitation plate to mount a hydrofoil will void the warranty on my motor. I guess I'll have to wait until November 11, 2002 before going through with this idea. Thanks, Gary, Tom, Corey, and Esox! Appreciate the help.



Mark
 
I'd really like to hear from someone in the know about this -- I can't believe that a properly drilled hole in the cavitation plate would void your warranty. It has NOTHING to do with the internal workings of the motor.



That would be like voiding the warranty on your car if you installed an aftermarket stereo!



Neeley - you got any accurate info?



me!
 
I'm with Scott on this one. Doesn't make sense that a fin would void a warranty. Sounds like those that say if you don't use Mercury oil during the warranty period you'll void the warranty. Mercury know if they were to say that about the oil, they'd have to supply the oil at no coat to the consumer.
 
The post I was referring to earlier state that the Merc warranty is voided when any kind of modification is made to the unit. I'll see if I can find the link and post it here.



Mark
 
Here is Mercury Marine's opinion on using stabilizer fins, or hydrofoils (off of their web site):





General FAQs

Q: Can I use aftermarket "fins" to help my boat get on plane faster?



A: Using a product often referred to as a stabilizer fin is a modification of the gearcase that may change the manner in which the boat operates on the water. With the unit trimmed fully down (in or under), a reduction of the time necessary to get a boat on plane may result. However, some V-bottom boats using a stabilizer fin may exhibit a tendency to roll over far to one side as soon as planing occurs. The direction and degree of the roll will be dictated by prop rotation, weight distribution, and degree of trim under. The boat roll can cause passengers to be ejected. Trimming up or out can reduce or eliminate the roll. Because it is not possible to know how a given boat will respond to the use of such a product without thorough testing, Mercury cannot recommend that such products be used or not used. Also, use of these products may cause or contribute to the failure of the anti-ventilation plate on the gearcase. Failures caused, or contributed to, by modification are not covered by the limited warranty.

 
OK...... THAT is reasonable and fair.



You drill the holes and the cavitation plate breaks - it's your baby.



You drill the holes and the motor blows - it's theirs.
 

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